The present invention relates to extensible non-wovens, such as those used, for example, as components in elastic components for personal hygiene products such as diapers and pants. The invention in particular relates to extensible non-wovens using hydroentangled staple fibers, a method for producing respective non-wovens and an elastic multilayer laminate using the non-woven.
Elastic components for personal hygiene products comprise, for example, a diaper ear attached to the diaper chassis. Located on the diaper waistband is the so-called landing zone. This is the counterpart to which the hook material gets caught mechanically when closing the diaper. The diaper ear is according to prior art composed of a multi-layer laminate which is according to prior art fixed thermally or by way of ultrasound to one side to the diaper chassis at the rear. Furthermore, hook material is also attached thermally at the open side of the ear facing the diaper waistband.
To increase wearing comfort and fit, these laminates contain elastic components, frequently films which after closing the diaper allow adaptation of the diaper waistband to the body shape due to the restoring force of the plastic portion. In order to provide the user with an appealing haptic feel, the elastic components are frequently on one or on both sides covered with textile cover sheets made of non-woven.
Tests have shown that the user when closing a diaper requires a force on the diaper ear in the range of max. 10N. The tensile force is there commonly in the range of 0-100%. After loss of the tensile force, the diaper ear must again largely restore shape due to its elasticity. This range between 0 to 10N force and 0-100% elongation is also referred to as the functional region.
Materials suitable for this are mostly composed of a laminate in which an elastic layer is at least on one side covered with a cover sheet. The bond between the layers can there be effected by way of adhesive or thermal lamination.
The following requirements therefore arise for a suitable cover sheet:
a. slight inclination of the force-elongation curve in the functional region when loading in the transverse direction
b. longitudinal stability, so that only a small width change occurs during processing
c. few process steps in the diaper ear production
d. no shedding fibrous material during use
e. low dust formation during processing
f. stop function for preventing overstretching
g. low thickness to realize economic roll run times
h. sufficient thermal sealing to ensure good bonding strength to the chassis of the diaper or pants and the hooks.
The systems in principle established in the market are described, for example, in the article “Performance and Fit” by the authors Dr. Hornfeck and Bernhuber, Non-woven Industry, January 2013 pages 56 to 62. In particular the advantages of hydroentangled non-woven materials are pointed out.
Cover sheets can be composed, for example, of thermally calendar-entangled staple fiber non-wovens. EP 2069141 B1 is there generic. An activatable zero strain composite laminate web is known from this document, comprising an activatable elastic laminate web and at least one pre-bonded staple fiber non-woven web. The activatable elastic laminate web comprises an elastic core layer and a skin layer which is less elastic than the core layer. The staple fiber non-woven web is attached to one of the skin layers of the elastic laminate web and has an elongation at fracture of at least 100% in the cross-direction. The activatable elastic laminate web forms an essentially homogeneous microtextured surface when stretched in the first upload past the elastic limit of the one or more skin layers.
Characteristic for such staple fiber non-wovens is a force-elongation behavior in MD and CD as shown in FIGS. 1 and 2. The bonding area in the calender is between 8 and 22%. Due to this thermal bonding, the portion of fibers corresponding to the bonding area is in the non-woven melted to each other and thereby fixed in the non-woven composite. Such non-wovens have sufficient stability in the longitudinal direction despite good extendibility in the transverse direction so that product stress fluctuations in the longitudinal direction have little effect on the width. Such non-wovens are therefore also thin enough to produce large roll lengths, which has a positive effect on the efficiency of further processing.
A drawback of staple fiber non-wovens thus produced is that they build up a force-elongation curve in CD in the functional region of the diaper ear that is too steep as compared to the elastic component, which is by the user perceived as being negative.
Laminates using staple fiber non-wovens that are thermally calendar bonded are in an additional process step commonly activated. This activation represents an overelongation of the material in the transverse direction with the purpose to break up a large part of the existing bindings so that the force to be exerted in subsequent use to stretch the diaper ear is as low as possible. This activation takes place in the laminated state, i.e. together with the elastic component, but can also take place beforehand. A drawback is that these non-wovens are there damaged in their structure such that the fibers forming the non-woven are no longer completely held in the non-woven. As a result, the fibers can escape from the non-woven and be shed; delamination is also possible. Furthermore, the non-woven contributes no strength-enhancing features to the diaper ear.
It arises based on the above-mentioned requirement profile that thermally calendar-bonded non-wovens do satisfy requirements b, e and g stated above, but doe not satisfy the other requirements.
EP 1921192 B1 describes the use of water-jet bonded filament or staple fiber non-wovens for the same purpose of application. Due to the water-jet bonding, the bonding points of the fibers among each other are not rigidly fixed but are flexible. A force-elongation curve typical for such material is shown in FIG. 1, curve 1. The required activation process can be omitted when using such non-wovens.
The fibers are by water-jet needling reoriented such that the original two-dimensional fiber alignment is converted into a three-dimensional fiber orientation. The fibers are therefore more firmly incorporated into the non-woven and the risk of dust formation during processing or shedding during use is minimized.
The drawback of such hydroentangled non-wovens is that they have a greater thickness than the aforementioned calender-bonded non-wovens. As a result, the rolls have a lower run length which makes more frequent roll changes necessary and results in additional costs. Furthermore, the water-jet bonded non-wovens exhibit a higher elongation in the longitudinal direction of the material as compared to calendar-bonded non-wovens and are therefore harder to process because small fluctuations in web tension already cause width contractions and therefore lead to discharge due to the lack of required width.
The object of the present invention is therefore to avoid the above described drawbacks of prior art.